Shopping cart price updated, failure when loaded from db

I have an ecommerce site with a custom mvc to add the product to
shopping cart, just so that I can use a back-system (ERP) to calculate
the price. This is done by a WCF service and it sets the cart details
price to recieved value.
It all works fine, unless when I have a
shopping cart and the session dies. Then when Sitefinity tries to get
the shoppingcart by using the cookie, I will get a "You cannot add this
item to your cart as the price of the item is less than zero." error.
I'm guessing that sitefinity is trying to recreate the shopping cart and
get the price from the product in sitefinity (=0)

First of all, is my analysis correct?

Can I somehow modify how Sitefinity updates the price when recreating the shopping cart so I can use the WCF service there also?

If that's not possible, is there a way to disable sitefinity to NOT remember shopping cart when session dies?

  You cannot add this item to your cart as the price of the item is less than zero.


Exception:

Description: An unhandled exception occurred during
the execution of the current web request. Please review the stack trace
for more information about the error and where it originated in the
code.

Full stacktrace

[ArgumentException: You cannot add this item to your cart as the price of the item is less than zero.]
Telerik.Sitefinity.Modules.Ecommerce.Orders.OrdersManager.UpdateProductInformationInCartDetails(CartOrder cartOrder) +2273
Telerik.Sitefinity.Modules.Ecommerce.Orders.Web.UI.ShoppingCartSummaryViews.ShoppingCartSummary.MakeCartItemsHaveLatestProductInfo(CartOrder shoppingCart) +79
Telerik.Sitefinity.Modules.Ecommerce.Orders.Web.UI.ShoppingCartSummaryViews.ShoppingCartSummary.OnPreRender(EventArgs eventArgs) +407
System.Web.UI.Control.PreRenderRecursiveInternal() +113
System.Web.UI.Control.PreRenderRecursiveInternal() +222
System.Web.UI.Control.PreRenderRecursiveInternal() +222
System.Web.UI.Control.PreRenderRecursiveInternal() +222
System.Web.UI.Control.PreRenderRecursiveInternal() +222
System.Web.UI.Control.PreRenderRecursiveInternal() +222
System.Web.UI.Control.PreRenderRecursiveInternal() +222
System.Web.UI.Control.PreRenderRecursiveInternal() +222
System.Web.UI.Control.PreRenderRecursiveInternal() +222
System.Web.UI.Control.PreRenderRecursiveInternal() +222
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +4297